JP-B2-2877145 discloses an example of a known apparatus for activating an air bag device such that the output of the activated air bag is suitably selectable between high and low values. This known apparatus uses a floor sensor disposed in a floor tunnel located in a central portion of an automotive vehicle, for detecting a deceleration value of the vehicle in its longitudinal direction, and calculating a value of a suitable control parameter on the basis of the detected vehicle deceleration value. The apparatus is arranged to select the high output or low output of the air bag device, according to a result of a comparison of the calculated the control parameter value with a predetermined threshold value. The known apparatus described above permits the air bag device to be activated so that the operator or passenger of the vehicle is effectively protected against an impact to be applied to the vehicle upon its collision.
However, the threshold value used to select the high or low output of the air bag device upon a head-on collision of the vehicle and that used upon an irregular collision of the vehicle should be different from each other. The use of a single threshold value in the known apparatus described above does not permit adequate selection of the output of the air bag device depending upon the type of the collision of the vehicle.